Okay, here's something that I'm pretty sure can deal with both Chansey and Suicune, and has a decent matchup against Doublade and Rhydon. It's niche, to say the least, but given how many offensive teams have trouble with those first two, I'd argue that it might be warranted.
Gallade @ Leftovers
Ability: Prankster
EVs: 240 HP / 252 Atk / 16 Spe
Adamant Nature
- Substitute
- Swords Dance
- Focus Punch
- Foresight
This inherits from Riolu. It will:
- Outspeed all Chanseys -- even those Pranksters that run 252 Speed. If you're not worried about 252 Speed Chansey (I'm not, but why risk it?), move the EVs to HP.
- Proceed to Substitute and set up on said Chanseys, destroying them with Focus Punch. This also blocks Transform.
252+ Atk Gallade Focus Punch vs. 252 HP / 252+ Def Eviolite Chansey: 696-818 (98.8 - 116.1%) -- 87.5% chance to OHKO
- After a Swords Dance, 2HKO Intimidate Suicune through Intimidate.
+1 252+ Atk Gallade Focus Punch vs. 252 HP / 252+ Def Suicune: 256-303 (63.3 - 75%) -- guaranteed 2HKO after Leftovers recovery
- Set up Substitutes on +0 Suicune.
4 SpA Suicune Scald vs. 240 HP / 0 SpD Gallade: 70-84 (20.7 - 24.9%) -- guaranteed 5HKO
4 SpA Suicune Ice Beam vs. 240 HP / 0 SpD Gallade: 53-63 (15.7 - 18.6%) -- possible 6HKO (The Ice Beam concern is why I didn't use Breloom, which tanks Scalds with much less HP investment)
Of course, if you can get the switch-in, Suicune is much easier.
Now, this has a bit more trouble with Doublade, which is where Foresight comes in: Foresight into Focus Punch is actually stronger than two Shadow Claws, and this nets you the OHKO at +2:
+2 252+ Atk Gallade Focus Punch vs. 252 HP / 252+ Def Eviolite Doublade: 374-444 (116.1 - 137.8%) -- guaranteed OHKO (after Foresight)
+2 252+ Atk Gallade Shadow Claw vs. 252 HP / 252+ Def Eviolite Doublade: 118-140 (36.6 - 43.4%) -- guaranteed 3HKO
The problem here is, of course, that Doublade can break your substitutes without breaking a sweat, and you
need a few turns to break it. It does mean, though, that Doublade is not a defensive check if you've managed to set up a Swords Dance.
Oh, and it 2HKOs Rhydon with no boosts:
252+ Atk Gallade Focus Punch vs. 252 HP / 252+ Def Eviolite Rhydon: 222-264 (53.6 - 63.7%) -- guaranteed 2HKO
+2 252+ Atk Gallade Focus Punch vs. 252 HP / 252+ Def Eviolite Rhydon: 440-522 (106.2 - 126%) -- guaranteed OHKO
Note that Hariyama is an option if you want to narrowly avoid the 2HKO from Rhydon's Earthquake while still tanking Suicune's Scalds (252+ Atk / 40 Def / 212 SpD / 4 Spe is the spread for that), but then you're risking a speed creep with Chansey, and I personally prefer the reliability of that matchup.
As a mono-attacking set, Gallade will have trouble breaking through natural Fighting-resists and paired Ghost-types, and faster priority users can obviously prey on it, and Unaware can wall it. I also suspect that it will be pretty underwhelming against offense, unless it's particularly slow offense. Nonetheless, I think handling a number of the tier's best physical walls should make it viable, no?
(None of this to say is that Chansey shouldn't be banned. It should. I'm just thinking up stopgaps that aren't untenably niche)